The grids of a lead-acid accumulator perform two main functions: they conduct electrical current, and they retain the active material. They also have to stand up well to being immersed in sulphuric acid in order to ensure long battery life. Further, if they are made from material that possesses high hydrogen overvoltage, the battery can require little or no maintenance.
From the chemical and the electrochemical points of view, soft lead is a very good material for making negative grids, but its use is limited by its very poor mechanical properties.
That is the reason why most conventional grids are made of lead alloys that are much stronger mechanically than is pure lead. Nonetheless, the use of such alloys gives rise to grids which are relatively heavy and in which the chemical and electrochemical properties of soft lead are not fully conserved. Thus, in particular, hydrogen overvoltage or self discharge, is degraded, and this may be a handicap, particularly in starting or traction batteries.
Proposals have also been made to make grids by covering a plastic support with a conductive material, but this causes problems when it comes to soldering or welding the electrical terminal or tab of the grid to a current collector.
Grids can also be made by by sewing conductive threads to an inert felt, or by using alumina fibres which have been specially treated and impregnated with lead, but such solutions are relatively complex to put into effect, and are difficult to adapt to continuous manufacture on an industrial scale.
Finally, U.S. Pat. No. 4,134,192 describes method of making grids using cloth obtained by weaving insulating threads together with interlaced conducting threads along the warp and/or the weft. However, grids made in this way do not have adequate mechanical properties, particularly where rigidity is concerned.
Preferred implementations of the present invention mitigate the above-mentioned drawbacks, and in particular the invention can be used to provide a very light grid having remarkable mechanical characteristics.